theorem proved term proof

`phi_pos`

No prose has been written for this declaration yet. The Lean source and graph data below render without it.

formal statement (Lean)

 120theorem phi_pos : 0 < phi := by

proof body

Term-mode proof.

 121  unfold phi
 122  have h : 0 < Real.sqrt 5 := Real.sqrt_pos.mpr (by norm_num : (0:ℝ) < 5)
 123  linarith
 124
 125/-- φ² = φ + 1 (the defining property). -/